Trenching apparatus and a method of trenching

ABSTRACT

A trenching apparatus, includes a body moveable on the ground surface, a ground engagement boom associated with the body, the boom being movable when engaged with the ground to form a trench; a lifting system arranged to control and configure the ground engagement boom so as to enter the ground; in which the ground engaging boom is an endless chain ground-engaging boom, including a main body and a chain tensioner coupled to the main body at or close to the upper end thereof.

The present invention relates to trenching apparatus and a method oftrenching.

There are many known trenching machines for digging trenches in soil byuse of a prime mover such as a crawler tractor, or a conventionaltractor pulling a trailer, in which a cutting device is positioned inthe trench on a boom. The main examples are a cutting rotor rotatingabout an axis transverse to the trench, known as a ripper cutter, or oneor more cutting rotors rotating about an axis aligned along the lengthof the boom, generally known as a milling cutter, or a cutting devicehaving an elongate endless support means carrying a plurality of cuttingelements and trained along upper and lower runs on the boom, known as achain cutter. Where a cutting rotor is used this is mounted on thedistal end of a boom projecting forwardly and downwardly from the primemover, relative to the direction of digging of the trench. Where a chaincutter is used, this is normally mounted on a boom extending downwardlyand rearwardly from the prime mover relative to the direction of cuttingof the trench.

Examples of such trenching machines are found in, for example,CH-A-239498, WO-A-95/13433, WO-A-03/044286, U.S. Pat. No. 6,467,201,EP-A-080,802, CN-A-2010 50077, CN-A-2517789, GB-A-786,829,WO-A-2007/035,400, JP-H04169696, U.S. Pat. No. 5,540,006, GB-A-972,208,GB-A-848,277, GB-A-735,116, U.S. Pat. No. 6,470,607, GB-A-1,118,907,GB-A-2,088,930, GB-A-155,766, GB-A-2,551,419 and WO-A-2012/123,622.

There are also known types of trenchers that are arranged to utilize avertical cutting boom. Examples include trenchers provided by SoletancheBachy. In particular, one example of equipment provided by SoletancheBachy suitable for deep trenching is known as the TM-80.

One known system for trenching is provided by Hayward Baker Inc and isknown as Trench cutting and Remixing Deep (TRD) Soil Mix Walls. Thesystem is described athttps://www.haywardbaker.com/uploads/solutions-techniques/trd-soil-mix-walls/Hayward-Baker-TRD-Brochure.pdf.As explained in this reference, the system utilizes a sectional verticalcutter made of cutter post sections that are assembled in situ.

In some situations, improvements in relation to deep trenchers arerequired.

According to a first aspect of the present invention there is provided atrenching apparatus, comprising: a trencher body moveable on the groundsurface, and a ground engagement boom associated with the trencher body;

lifting means arranged to control and configure the ground engagementboom so as to enter the ground in a substantially verticalconfiguration;

selectively configurable support legs moveable between a first closedposition and a second deployed configuration in which the legs areextended in a direction away from the body of the apparatus to providesupport to the trenching apparatus when the boom is configuredvertically and not engaged with the ground.

In an embodiment, the boom is movable in a substantially vertical planewhen engaged with an end surface of the trench. In an embodiment, thetrencher body is moveable on the ground surface above the level of thetrench.

In contrast to known methods the present invention utilizes support legsto enable a simple vertical angle of attack for a ground engaging boomin a trenching machine. Compared for example to the TRD Soil Mix wallmethod of Hayward Baker this provides significant advantages.Importantly there is no need for a complex method of modular boomconstruction so as to enable the base unit that supports and controlsthe cutter to maintain a low profile. Due to the stability provided bythe support legs, it is no longer necessary to ensure that the base unithas a low profile.

In an embodiment, the lifting means is arranged to control and configurethe ground engagement boom so as to enter the ground from above.

In an embodiment, the ground engagement boom is a cutting boom forcutting earthen material from the end surface of the trench.

In an embodiment, the cutting boom is an endless chain cutting boom.

In an embodiment, the ground engagement boom is a mixing boom for mixingagent such as (but not limited to) cement or bentonite with earth withinthe trench.

In an embodiment, the longitudinal length of the ground engagement boomis between 10 and 20 metres.

In an embodiment, the ground engagement boom weighs between 10 and 20tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the support legs are pivotally mounted to the body soas to be selectively reconfigurable between the closed and extendedconfigurations.

In an embodiment, the support legs are telescopically mounted so as tobe slidably configurable between the first closed and second deployedconfiguration.

In an embodiment, the legs have a first longitudinal section and asecond longitudinal component configured telescopically with respect tothe first longitudinal section, and wherein the first longitudinalsection is coupled to the body of the prime mover and when extended inthe second deployed configuration the second longitudinal componentslides out of the first longitudinal component.

In an embodiment, the second longitudinal component has at its distalend a downwardly deployable longitudinal support member.

In an embodiment, each of the downwardly deployable longitudinal supportmembers has a foot removably fixable thereto, for engagement with theground.

In an embodiment, when in the deployed configuration, the support legsincrease the overall envelope of the footprint of the trenchingapparatus by at least 150%, and preferably 200%, as compared to when thelegs are in the first closed configuration.

In an embodiment, the trenching apparatus comprises tracks for movingthe trenching apparatus when the legs are in the first closedconfiguration.

According to a second aspect of the present invention, there is provideda method of trenching, using trenching apparatus having a trencher bodymoveable on the ground, and a ground engagement boom associated with thetrencher body, the boom being movable in a substantially vertical plane,and lifting means arranged to control and configure the groundengagement boom so as to enter the ground from above in a substantiallyvertical configuration the method comprising;

extending the legs in a direction away from the body of the apparatus toprovide support to the trenching apparatus when the boom is configuredvertically and not engaged with the ground.

In an embodiment, the lifting means is arranged to control and configurethe ground engagement boom so as to enter the ground from above in asubstantially vertical configuration.

According to a third aspect of the present invention there is provided atrenching apparatus, comprising: a body moveable on the ground surface,and a ground engagement boom associated with the body, the boom beingmovable when engaged with the ground to form a trench; lifting meansarranged to control and configure the ground engagement boom so as toenter the ground and to configure the boom to an inclined orientation inwhich the boom extends at least partially over the body of theapparatus;

a protection chute provided on the body to protect the body frommaterial that falls from the boom, when the boom is in the inclinedorientation.

A trenching apparatus is provided that includes a chute positioned toensure that material that falls from the boom when in an inclinedposition does not fall onto the apparatus thereby damaging it.Conventionally to perform repairs or cleaning on a ground engaging boomwhilst limiting risk of damage to the apparatus, it has been necessaryto remove the boom from the apparatus and thereby perform the necessarywork at a remote or separate location. In the present trenchingapparatus the boom is positioned in an inclined position which can besubstantially within the footprint of the apparatus during maintenanceand/or cleaning.

In an embodiment, the ground engagement boom is a cutting boom forcutting earthen material from the end surface of the trench.

In an embodiment, the cutting boom is an endless chain cutting boom.

In an embodiment, the ground engagement boom is a mixing boom for mixingcement mixing agent such as (but not limited to) cement or bentonitewith earth within the trench.

In an embodiment, the longitudinal length of the ground engagement boomis between 10 and 20 metres.

In an embodiment, the ground engagement boom weighs between 10 and 20tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the chute is sized to receive the entire part of theboom that extends over the body of the trenching apparatus when theground engagement boom is in the inclined orientation.

In an embodiment, the chute is supported by arms fixed to the body ofthe trenching apparatus.

In an embodiment, the chute is orientated at an angle to the horizontalplane of the trenching apparatus.

In an embodiment, the angle is between 10 and 45 degrees.

In an embodiment, the trencher comprises at its end, e.g. its rear end aboom engagement cage for controlling the depth in the ground or heightrelative thereto at which the boom is positioned.

In an embodiment, the boom engagement cage comprises a continuationchute which when the boom is in the inclined orientation forms acontinuous channel with the protection chute.

In an embodiment, the trenching apparatus comprises water or fluidoutlets such as jets to direct and cause fluid to flow along theprotection chute when the boom is arranged therein.

According to a fourth aspect of the present invention, there is provideda method of trenching which could include trench digging or mixing,using a trenching apparatus comprising a body moveable on the groundsurface, and a ground engagement boom associated with the body, the boombeing movable when engaged with the ground to form a trench; liftingmeans arranged to control and configure the ground engagement boom so asto enter the ground and to configure the boom to an inclined orientationin which the boom extends at least partially over the body of theapparatus, the method comprising: providing a protection chute on thebody to protect the body and/or the apparatus from material that fallsfrom the boom, when the boom is in the inclined orientation.

According to a fifth aspect of the present invention there is provided atrenching apparatus, comprising: a body moveable on the ground surface,a ground engagement boom associated with the body, wherein the groundengagement boom comprises a chain for interacting with earth in use;lifting means arranged to control and configure the ground engagementboom so as to enter the ground and to configure the boom to an inclinedorientation in which the boom extends at least partially over the body;a winch provided on the body to engage with the chain of the groundengagement boom when in the inclined orientation.

In an embodiment, the ground engagement boom is movable in asubstantially vertical plane.

There is provided a trenching apparatus in which a winch for changingthe chain on a chain cutting or mixing boom is provided on the trenchingapparatus (or body thereof) itself, and not on the boom itself.Positioning of the winch in the present system on the body of themachine or apparatus itself enables and ensures that a chain can easilybe changed on the ground engaging boom irrespective of the size of theground engaging boom and the associated size and weight of the cuttingchain itself.

In an embodiment, the ground engagement boom is a cutting boom forcutting earthen material from the end surface of the trench.

In an embodiment, the ground engagement boom is a mixing boom for mixingan agent such as (but not limited to) cement with earth within thetrench.

In an embodiment, the longitudinal length of the ground engagement boomis between 10 and 20 metres.

In an embodiment, the ground engagement boom weighs between 10 and 20tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the apparatus comprises a protection chute provided onthe body of the trencher to protect the body from material that fallsfrom the boom and to support the boom in the inclined orientation.

In an embodiment, the apparatus comprises a spool with a cable having anend connector for engagement with the end of a replacement chain to beput on the ground engagement boom when in the inclined orientation.

In an embodiment, the cable is routed via a shoulder on the distal endof the ground engagement boom to enable substantially the entire lengthof the ground engagement boom to be surrounded by the replacement chain.

In an embodiment, the shoulder comprises a pulley.

In an embodiment, the shoulder is slidably mounted on the body of theboom so that it can be moved from the top end to the distal end at whichend it can be used to change the chain on the boom.

A shoulder is provided slidably mounted on the boom for housing a pulleyor routing point for directing the cable of the winch used when changingthe chain on the boom. This means that the shoulder can be selectivelyrepositioned at appropriate times so that it is placed in position forchanging the chain only when needed and at other times can beappropriately positioned or stowed so as not to cause any possibleobstruction during normal use of the trenching apparatus.

In an embodiment, in the inclined orientation, the ground engagementboom is at an angle of between 10 and 45 degrees to the body of thetrencher.

According to a sixth aspect of the present invention, there is provideda method of putting a chain on to the ground engagement boom of atrencher, wherein the trencher comprises a body that is moveable on theground surface and a ground engagement boom associated with the body,and lifting means arranged to control and configure the groundengagement boom so as to enter the ground from above and to configurethe boom to an inclined orientation in which the boom extends at leastpartially over the body of the trencher, the method comprising,orienting the boom in the inclined orientation; engaging one of the endsof the chain with a cable of a winch provided on the body of thetrencher; activating the winch to pull the chain onto the groundengagement boom.

In an embodiment, the ground engagement boom is movable in asubstantially vertical plane.

There is provided a trenching method in which a winch for putting achain onto a boom, or changing the chain on a chain cutting or mixingboom, is provided on the trenching apparatus (or body thereof) itself,and not on the boom itself. Positioning of the winch in the presentsystem on the body of the machine or apparatus itself enables andensures that a chain can easily be changed on the ground engaging boomirrespective of the size of the ground engaging boom and the associatedsize and weight of the cutting chain itself.

In an embodiment, the cable is routed via a shoulder on the distal endof the ground engagement boom to enable substantially the entire lengthof the ground engagement boom to be surrounded by the chain.

The method can include moving e.g. slidably moving a shoulder or pulleymounted on the boom for directing the cable of the winch used whenchanging the chain on the boom. This means that the shoulder can beselectively repositioned at appropriate times so that it is placed inposition for changing the chain only when needed and at other times canbe appropriately positioned or stowed so as not to cause any possibleobstruction during normal use of the trenching apparatus.

According to a seventh aspect of the present invention there is provideda trenching apparatus, comprising: a body moveable on the groundsurface; a ground engagement boom associated with the body, the boombeing movable when engaged with the ground to form a trench; liftingmeans arranged to control and configure the ground engagement boom forengagement with the ground; in which the ground engaging boom is anendless chain ground-engaging boom, comprising a main body and a chaintensioner coupled to the main body at the upper end thereof.

By providing the chain tensioning mechanism on the ground engaging boomand particularly at or close to the top of the ground engaging boom itis possible to ensure that the tensioning mechanism is less likelyitself to go below the surface of the ground. Thus it can remainrelatively free of material from the ground.

Advantageously, the tensioning mechanism is remote from the lower end ofthe ground engaging boom which will be interacting on a more regularbasis with the earth formation being trenched. It is less likelytherefore to be damaged by impact on use.

Second, the tensioning mechanism is kept away from the section of theboom that is likely to be most engaged with the mixing agent such as(but not limited to) cement or bentonite mixing agent, such as cement orbentonite, when used as a mixing mechanism. It is known and conventionalto provide such tensioning mechanisms at the distal end of a groundengaging boom but it has been recognised that by providing thetensioning mechanism at the top end of the cutting boom the risk fromthe mixing agent being used setting and thereby possibly rendering thetensioning mechanism ineffective, is significantly reduced.

In an embodiment the lifting means is arranged to configure and controlthe ground engaging boom so as to enter the ground in a substantiallyvertical configuration.

In an embodiment, the chain tensioner comprises an arm pivotally coupledto the main body of the ground engagement boom.

In an embodiment, the arm is hydraulically controllable to move betweena first closed position in which its distal end is close to the mainbody and a second deployed position in which its distal end is movedaway from the main body to tension a chain arranged on the groundengagement boom.

In an embodiment, the apparatus comprises an endless chain mounted onthe main body.

In an embodiment, the chain is a cutting or mixing chain.

In an embodiment, the ground engagement boom weighs between 10 and 20tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the arm comprises a pinion at its distal end togearingly engage with the chain as it is driven around the groundengagement boom.

In an embodiment, the arm is between 1 and 3 metres long.

In an embodiment, the arm has a plurality of hydraulic drive cylindersprovided to hydraulically control the position of the arm with respectto the body.

In an embodiment, the chain tensioner is positioned with respect to themain body such that when the ground engaging boom is fully engaged withthe ground the chain tensioner is above ground surface.

According to a eighth aspect of the present invention, there is providedan endless chain ground-engaging boom, in which the ground engagingboom, comprises a main body and a chain tensioner coupled to the mainbody at or close to the upper end thereof.

As above with the trenching apparatus according to the first aspect ofthe present invention, by providing the chain tensioning mechanism onthe ground engaging boom and particularly at or close to the top of theground engaging boom it is possible to ensure that the tensioningmechanism is less likely itself to go below the surface of the ground.Thus it can remain relatively free of material from the ground. Also thetensioning mechanism is kept away from the section of the boom that islikely to be most engaged with the mixing agent, such as cement orbentonite, mixing agent such as (but not limited to) cement or bentonitewhen used as a mixing mechanism.

In an embodiment, the chain tensioner comprises an arm pivotally coupledto the main body of the ground engagement boom.

In an embodiment, the arm is hydraulically controllable to move betweena first closed position in which its distal end is close to the mainbody and a second deployed position in which its distal end is movedaway from the main body to tension a chain arranged on the groundengagement boom.

In an embodiment, the ground engaging boom comprises an endless chainmounted on the main body.

In an embodiment, the chain is a cutting or mixing chain.

In an embodiment, the ground engagement boom weighs between 10 and 20tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the arm comprises a pinion at its distal end togearingly engage with the chain as it is driven around the groundengagement boom.

In an embodiment, the arm is between 1 and 3 metres long.

In an embodiment, the arm has a plurality of hydraulic drive cylindersprovided to hydraulically control the position of the arm with respectto the body.

In an embodiment, the chain tensioner is positioned with respect to themain body such that when the ground engaging boom is fully engaged withthe ground the chain tensioner is above ground surface.

According to a ninth aspect of the present invention, there is provideda method of varying tension in the chain of a ground-engaging boom oftrenching apparatus, in which the trenching apparatus comprises a bodymoveable on the ground surface and a ground engagement boom associatedwith the body, the boom being movable when engaged with the ground toform a trench, the method comprising: controlling the tension of thechain using a chain tensioner coupled to the main body of the groundengaging boom at the upper end thereof.

According to a tenth aspect of the present invention there is provided atrenching apparatus, comprising: a body moveable on the ground surface,and a ground engagement boom associated with the body, the boom beingmovable when engaged with the ground to form a trench; a main powersupply to provide power to the apparatus; lifting means, powered by themain power supply, arranged to control and configure the groundengagement boom so as to enter the ground; an auxiliary power supplyarranged to provide power to the lifting means in the event of failureof the main power supply

In an embodiment, the lifting means is arranged to control and configurethe ground engagement boom so as to enter the ground from above in asubstantially vertical orientation.

There is provided a trenching apparatus including an auxiliary powersupply which can be used to provide power to the apparatus in the eventof failure of the main power supply of the apparatus. This is importantas it enables power to be provided in situations that might be timecritical such as when there is a power supply failure during trenching.This is particularly the case when trenching involves the use of somesetting material, such as cement or bentonite, to perform soil or groundmixing. In these situations if there is a failure of the main apparatuspower supply the ground engaging boom can be left for extended periodsof time within the environment of the recently mixed setting material.This can then cause the material to harden and set around the groundengaging boom which can then be impossible, or economically unfeasible,to retrieve in a reusable way from the ground.

The inventors have recognised that use of an auxiliary power supply willsolve this technical problem. Forming a trench can of course include theprocess of actually digging the trench so as to leave a an empty trenchin the ground, or indeed the mixing of a material, such as but notlimited to, cement with soil in so as to form a trench of mixed soil andmaterial.

In an embodiment, the lifting means is arranged to selectivelyreconfigure the boom from the substantially vertical orientation to aninclined orientation in which the boom extends at least partially overthe body of the apparatus

In an embodiment, the ground engagement boom is a cutting boom forcutting earthen material from the end surface of the trench.

In an embodiment, the ground engaging boom is an endless chain cuttingboom.

In an embodiment, the ground engagement boom is a mixing boom for mixingcement with earth within the trench. In an alternative, instead ofcement another mixing agent could be used. In other words the boom is aground engagement boom for mixing an agent in general and not limited tocement.

In an embodiment, the longitudinal length of the ground engagement boomis between 10 and 20 metres.

In an embodiment, the ground engagement boom weighs between 10 and 20tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the apparatus comprises a protection chute, to protectthe body of the apparatus from material that falls from the boom.

In an embodiment, the chute is sized to receive the entire part of theboom that extends over the body of the trenching apparatus when theground engagement boom is an inclined orientation.

In an embodiment, the auxiliary power supply is integrated with the bodyof the apparatus.

This embodiment provides the advantage that no separate components arerequired whilst still providing the effective redundancy of power supplywhich is useful in some specific situations as described above. Theauxiliary power supply will be a separate power circuit and pump but canbe built into or permanently coupled to the housing of the trenchingapparatus. The auxiliary power supply may be a hydraulic pump having aninlet conduit and an outlet conduit with connectors for connecting theinlet and outlet conduits to hydraulic power lines of the apparatus thatduring power supply from the main power supply are connected tohydraulic conduits of the main power supply.

In an embodiment, the auxiliary power supply is an independent separateunit connectable to the apparatus in the event of failure of the mainpower supply. This is advantageous as it can be supplied or provided (orreplaced) separately from the trenching apparatus itself. Again, as withthe integrated auxiliary power supply, the separate auxiliary powersupply may be a hydraulic pump having an inlet conduit and an outletconduit with connectors for connecting the inlet and outlet conduits tohydraulic power lines of the apparatus that during power supply from themain power supply are connected to hydraulic conduits of the main powersupply.

In an embodiment, the main power supply is a hydraulic pump arranged topump hydraulic fluid along hydraulic power lines to operate the liftingmeans.

In an embodiment, the auxiliary power supply is a hydraulic pumparranged to pump hydraulic fluid along the hydraulic power lines whenthere is a failure of the main power supply to the boom.

In an embodiment, the hydraulic pump of the auxiliary power supply hasan inlet conduit and an outlet conduit with connectors for connectingthe inlet and outlet conduits to the hydraulic power lines.

According to a eleventh aspect of the present invention, there isprovided a method of operating a trenching apparatus, wherein theapparatus comprises a body moveable on the ground surface above thelevel of a trench, and a ground engagement boom associated with thebody, the boom being movable when engaged with the trench, a main powersupply to provide power to the apparatus and lifting means, powered bythe main power supply to control the ground engagement boom so as toenter the ground, and an auxiliary power supply, the method comprising:in the event of failure of the main power supply providing power to thelifting means from the auxiliary power supply.

In an embodiment, the lifting means is arranged to control and configurethe ground engagement boom so as to enter the ground from above in asubstantially vertical orientation.

There is provided a trenching method including an auxiliary power supplywhich can be used to provide power to the apparatus in the event offailure of the main power supply of the apparatus. This is important asit enables power to be provided in situations that might be timecritical such as when there is a power supply failure during trenching.This is particularly the case when trenching involves the use of somesetting material, such as cement or bentonite, to perform soil or groundmixing. In these situations if there is a failure of the main apparatuspower supply the ground engaging boom can be left for extended periodsof time within the environment of the recently mixed setting material.This can then cause the material to harden and set around the groundengaging boom which can then be impossible, or economically unfeasible,to retrieve in a reusable way from the ground.

The inventors have recognised that a method of using an auxiliary powersupply will solve this technical problem.

In an embodiment, the main and auxiliary power supplies comprisehydraulic power supplies and the method comprises, in the in the eventof failure of the main power supply, disconnecting the main hydraulicpower supply from the apparatus and connecting hydraulic fluid conduitsof the auxiliary power supply to the apparatus to thereby power theapparatus.

In an embodiment, the auxiliary power supply is integrated with the bodyof the apparatus.

In an embodiment, the auxiliary power supply is an independent separateunit connectable to the apparatus in the event of failure of the mainpower supply.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawings in which:

FIGS. 1 and 2 are a schematic views of a known trenching apparatus;

FIG. 3 is a schematic view of component parts of a vertical chaincutting trencher;

FIG. 4 is a schematic view of the trencher FIG. 3, assembled prior toengagement of the ground engaging boom with the ground;

FIG. 5 is a schematic view of the trencher in FIG. 4 with the groundengaging boom at full depth in the ground;

FIG. 6 is a schematic view of the trencher machine on a trailer arrivingat a trenching site;

FIG. 7 is a schematic view of the machine of FIG. 6 with support legsextended;

FIG. 8 is a schematic view of the machine of FIG. 7 with support legsextended and feet lowered;

FIG. 9 is a schematic view of the machine of FIG. 8 with tracks providedon the machine;

FIG. 9a is a schematic view of the machine of FIG. 9, with the trailerremoved;

FIG. 10 is a schematic view of the machine of FIG. 9A with the legs in aclosed position;

FIG. 11 is a schematic view of the machine of FIG. 10 with hydraulicreels provided thereon;

FIG. 12 is a view of the machine of FIG. 11 with a protective chuteprovided thereon;

FIG. 13 is a view of the machine of FIG. 12, assembled with the groundengaging boom prior to engagement of the ground engaging boom with theground and prior to connection of the boom to hydraulic lines;

FIG. 14 is a view of the machine of FIG. 13 with the ground engagingboom lowered for connection of chain drive services such as hydrauliclines;

FIG. 14A is a view of the machine of FIG. 14 with the ground engagingboom partly submerged, i.e. at an intermediate trenching depth;

FIG. 15 is a view of the machine of FIG. 14A with the ground engagingboom at full trenching depth;

FIG. 16 is a detailed view of the machine including the ground engagingboom cradle;

FIG. 17 is a schematic view of the machine showing the boom cradle open;

FIG. 18 is a schematic view of the machine with the boom cradle openwithout a cutting boom assembled therein including a chute extension;

FIG. 19 is a representation of the machine with a ground engaging boomin position but no cutting chain installed;

FIG. 20 is a view of a close-up of the top of the ground engaging boom.

FIG. 21 is a schematic view of a machine including an auxiliary powersupply; and

FIG. 22 is a view of a trenching machine including an auxiliary powersupply unit.

FIGS. 1 and 2 show schematic views of a known trenching apparatus. It isa trench cutting apparatus as described in EP-A-0080802, for cutting atrench in rock.

Two crawler chassis 3 and 5 are coupled together by tie bars 7, the rearcrawler 3 having a cutting boom 2 pivotally mounted at 6. The forwardend of the boom 2 has a cutting boom 2 pivotally mounted at 6. Theforward end of the boom 2 has a cutting rotor 7 driven in rotation aboutan axis transverse to the trench to be cut. The distal end of the boom 2is coupled to the forward crawler 5 by a telescopic control arm 8comprising a hydraulic ram and telescopically extending sleeves coupledto the boom 2 by a coupling 9. In operation the machine is positioned tostraddle the line of the trench and the boom 2 is lowered into contactwith the ground. The cutting head 7 is rotated while applying force byway of the hydraulic ram 8 to move the cutting head 7 on an arcuate pathdownwardly and to remove rock from the forward end of the trench. Anendless chain conveyor 4 is positioned behind the cutting rotor 7 andthe spoil is carried away. The boom 2 is then raised and the machinemoved forward and the process is repeated.

Although the trenching apparatus described above works well, there is aneed for a trenching apparatus that is able to cut a deeper trench. Thishas application in fields such as the building of trenches in riverbanksfor example. Such trenches may be built for the purpose of the creationof water-impermeable barriers or for strengthening the structure of theground, for example, by mixing earth from the trench region with cement,thereby forming a hardened vertical wall within the ground where thetrench is formed. As used herein, the term trenching includes the use ofground engaging members both for cutting trenches in the ground and alsofor mixing of the earth or material within a trench as might be done forexample where cement or some other material is mixed with soil tocontrol various physical properties of the ground.

Accordingly as used herein, the term “ground engaging member” or “groundengaging boom” is to be understood as relating to a member thatgenerally engages with the ground which could include either cutting orforming a trench within the ground or mixing cement or other mixingmaterial such as bentonite, within a trench with the soil in the trench.Indeed considering these two specific examples, either could be referredto as “trenching” and in both cases a trench is formed.

FIG. 3 shows a disassembled schematic view of a trenching apparatus forsuch purpose.

The apparatus includes a trenching machine 10 arranged to receive aground engaging boom 12 which may be a cutting boom and importantlywhich can be inserted into the ground in a vertical orientation. Such avertical cutting boom trenching machine has particular advantage in thatthe ground engaging boom can be inserted into the ground effectivelywithin the footprint of the machine itself, i.e. without requiring spaceoutside of the footprint for a cutting arc.

Vertical insertion typically means that the movement of the groundengaging boom is translationally downwards rather than, say pivoted butit need not require that the boom extends and enters the ground atprecisely 90 degrees to the ground surface. Typically an angle of attackof the ground engaging boom, i.e. the angle that the longitudinal axisof the ground engaging boom makes to the surface of the ground, will be±10% to the vertical. More preferably the angle of attack is ±5 degreesto the vertical and most preferably it is vertical.

In the examples shown, the ground engaging boom 12 includes a cuttingchain 14 which has the function both of cutting a trench and, in thisexample, also due to the features and elements 16 on the chain providinga mixing function, for mixing an agent such as (but not limited to)cement that may be provided in the trench with the surrounding earth. Asexplained above such a process has the advantage in that a barrier ofreduced porosity or water permeability can be created which in areassuch as those close to river or canal banks is desired.

The trenching apparatus 10 includes tracks 18 and jack legs 20, whichprovide a significant technical function to this specific type oftrenching machine in accordance with a disclosed embodiment, and as willbe described in greater detail below.

A protective chute 22 is provided arranged, in use, and as will bedescribed in greater detail below, to couple with a chute section 24provided as part of a boom cradle 26. The protection chute 22 may alsobe used for other functions such as washing the ground engaging boomwhen it is not engaged with the ground.

An engine and control module 28 is provided in which a driver oroperator may sit to control the apparatus 10 in use.

Hydraulic reels 30 are provided which are arranged on the main body 34of the machine 10, arranged to be driven by a main hydraulic powersupply (not shown) within the main body 34. The main hydraulic powersupply is also arranged to provide power to drive the movement of theground engaging boom 12 by powering a pinion 40 (see FIG. 18), to bedescribed below. The main hydraulic power supply may typically be ahydraulic pump having an inlet and an outlet and being arranged andconfigured to pump hydraulic fluid to provide power as required. Anysuitable type of hydraulic pump can be used, as will be known to theskilled person.

The hydraulic reels 30 are provided, arranged to receive hydraulic fluidfrom the main hydraulic power supply and thereby to drive the cuttingchain 14. When the machine is assembled and operating in trenching mode,the hydraulic lines 30 are coupled to an upper end 36 of the groundengaging boom 12, as will be descried in greater detail below. Theground engaging boom 12 is provided with an integrated rack 38 arrangedin use to interact and be driven by the pinion 40 (see FIG. 18). Thepinion 40 is driven, in most cases by the main hydraulic power supplytoo and thereby controls the vertical position of the ground engagingboom 12 with respect to the cradle 26, and hence to the ground too.

FIG. 4 shows a schematic view of the trenching machine 10 arranged inposition ready for operation. In the example of FIG. 4, the groundengaging boom 12 is ready for engagement with the earth, but has not yetbeen driven into an engaged position. Hydraulic power is provided whichdrives the ground engaging boom down into the ground. As can be seen,the elements 14 (teeth in this case) at the lower end of the cuttingboom 12 are close to the ground, but have not yet broken the surface.The angle of attack of the ground engaging boom 12 is almost exactly 90degrees in the example shown. In addition due to the manner in which therack and pinion mechanism forming part of the cradle 26 operates, thedriving force will be in line with the boom and thus verticallydownwards.

The height of the boom 12 can be as required for the particular job,which could involve cutting and/or mixing a material in a trench, butpreferably is at least 10 metres long and more preferably between 15 and20 metres long. In particular, trenching operations, it is desired thatthe boom is at least 15 metres long. In such cases, the mass of theboom, including the cutting chain, in use, could be up to 30,000 KG. Aplurality of stabilising legs 20 are provided which function tostabilise the machine itself while, or during, the lowering of thecutting or mixing boom 12 into the surface of the soil takes place.

It has been recognised that in the example of vertical or near verticalimpact trenching machines such as that shown in FIGS. 3 and 4, astability providing mechanism flexibly or selectively reconfigurablyconnected to the housing 34 of the machine 10 provides a convenient andadvantageous mechanism for ensuring stability of the machine during thelowering of the trenching/mixing boom 12 into the surface of the soil.It has been recognised that although the centre of mass of the machinewill still be positioned above the footprint of the machine the heightof the boom itself can generate a lack of stability, particularly if,say the environment is one in which high winds can be present.

Although in known systems there is no suggestion or reason why stabilityproviding legs should be included (indeed it has previously been thoughtthat the boom itself when engaged with the ground is a source ofstability), it has now been recognised that they can provide asignificant advantage in terms of accounting for atmospheric conditionsand their effect on the machine's stability.

Referring to FIGS. 7 to 9 and 9A, the stability legs 20 comprise aproximal end 42 coupled to the machine and a distal end 44 from which avertically downwardly depending longitudinal support member 46 isarranged to extend. The legs 20 are selectively reconfigurable such thatthey can be folded (or telescopically collapsed) into close alignmentwith the machine 10 as shown in, say, FIG. 11 or 12, or provided in anextended configuration as shown in any of, say, FIGS. 7 to 9 and 9A. Insuch a configuration they are not in close alignment with the body orcan be said to extend away from a central longitudinal axis of themachine thereby increasing its stability. In extending away from acentral longitudinal axis of the machine the legs could be directionallysquare on to the axis or at some other angle whilst still extending awayfrom it and thereby extending the width. In one embodiment, the legs arenormal to the axis or at an angle of less than ±45 degrees to the normalto the longitudinal axis. The length of the legs when deployed can bevariable and selected to provide the required stability.

Feet 48 are provided as separate and connectable components which areprovided with an engagement region 50 for connection to the distal endof the downwardly depending longitudinal support member 46. In thisexamples, the downwardly depending longitudinal support members 46 arearranged to extend telescopically from an upper region 49. As will beexplained below, the legs 20 are used during the process of erection ofthe ground engaging boom 12 and lowering of the boom into the surface ofthe ground. Once the boom 12 has been lowered to a desired depth, therequirement for the extension of the legs 20 into the extendedconfiguration as shown in FIG. 7 is reduced. The boom 12 inserted intothe ground, itself provides a stabilising function and therefore thelegs 20 can be collapsed or retracted or removed.

As explained above, in one configuration, the legs may be pivotablyconnected to the machine 10 at the proximal end 42. In an alternativeembodiment, they may be removably and fixedly connected. In the exampleof FIG. 7, the shaping of the legs 20 can be seen. In particular, aswill be appreciated, there is an overlap region along the centrallongitudinal axis of the machine 10, wherein the legs in each of thefront and rear pairs overlap with each other. Looking again at FIG. 9,at the rear of the machine 10 there is a first pair of legs 52 and atthe front of the machine there is a forward pair of legs 54.

Each of the legs has a length that extends across the width of the bodyof the machine such that looking at the first pair of legs 52 it can beseen that the longitudinal body of the leg 56 extends under the machineand to the other transverse side. Still looking at the rear pair of legs52, the end 58 of the second leg of the pair (the foot of which cannotbe seen in FIG. 9) can be seen extending towards the opposite transverseside of the machine 10. Thus, there is overlap of the pair of legs inthe region of the body of the machine 10 as indicated by the arrow A.This ensures that the legs, when extended and engaged with the ground,through their interaction with the centre of mass of the body of themachine 10, provides significant stability to it.

In one example and in the specific example of FIGS. 7 to 9 and 9A, dueto the extension of the legs across the entire width of the body, thelegs may be formed of two telescopic sections such that there is anouter telescopic section 60 and an inner telescopic section 62 which,when in a closed configuration, will be positioned substantially withinthe length of the first telescopic section 60.

The use of such telescopically extending legs 20 ensures that stabilitycan be provided to the machine as a whole during insertion or loweringof the boom 12 into a trench for cutting or mixing. Typically wheneverthe ground engaging boom 12 is not engaged with the ground, i.e. notsubmerged below ground surface, the legs will be extended so as toprovide stability to the trenching apparatus.

Referring again to FIG. 3, the protective chute 22 will now bedescribed. The machine 10 includes an integrated protective chute 22which has a generally U-shaped cross-section. The position andconfiguration of the chute on the machine is so as to be able to preventfouling of the machine body 34 during the forward folding andtransporting of the ground engaging boom or cutting mechanism. Referringto, say, FIGS. 14 and 16, the chute 22 can be seen coupled to the body34 of the machine 10. Coupling arms 66 are provided to support the chute22 along its longitudinal extension.

As can be seen, the cradle 26 is included with a chute extension 24which, when the cradle 26 is in the upwards (folded) position as shownin FIG. 14 for transporting of the ground engaging boom 12, forms acontinuous channel with the fixed chute 22. The dimensions of the chute22 and the chute section 24 forming part of or associated with thecradle 26, are such that the end 68 of the chute 22 will fit within thedimensions of the end 70 of the chute section 24. Typically, the generaldimensions will be substantially the same, but the end 70 of the chutesection 24 may have a slightly enlarged width so as to accommodate thecross-section of the end 68 of the chute 22.

Looking again at FIG. 14, it can be seen that the chute and chutesection 24 when assembled, form a continuous channel within which atleast some of the cutting elements 14 of the chain are positioned. Thisassembly is particularly advantageous since it means that the chain 14and its cutting elements 16 can be easily washed by water or otherwashing fluid introduced to flow down the chute 22 under the force ofgravity and/or from pressurised fluid flow from an associated pump. Theconfiguration of the assembled chute 22 and chute section 24 ensuresthat washed or dropped cutting material from the chain 14 is directedaway from the machine and to a suitable place. Typically, the water andthe washings from the chain 14 may be directed into the trench that hasjust been cut or indeed onto the ground in a region where a trench willshortly be cut. In either case, the positioning of the washings isadvantageous in that it is away from the machine 10 itself andimportantly the cuttings or droppings from the chain do not fall ontothe machine.

In a preferred example, it could be that the chain is actually drivenwhen in the configuration as shown in FIG. 16 at the same time as apressurised flow or jet of water is directed down the down the chute andchute extension 24 such as to ensure that all cutting elements on thechain 14 of the boom 12 are washed. This means for washing the chain ofa chain cutter is advantageous as it is conveniently performed by themachine 10 itself and at least partially within the footprint of themachine itself.

Referring again to FIG. 3, a winch 80 is shown mounted on the machine10. The winch 80 is configured to function as a source of force to pulla chain onto the ground engaging boom when required. In known systems,such a winch may typically be provided on the ground engaging boomitself. It has been recognised that this may be disadvantageous giventhe weight of the ground engaging boom. The positioning of the winch inthe present system is on the machine 10 itself. As will be describedbelow, this ensures that a chain can easily be changed on the groundengaging boom irrespective of the size of the ground engaging boom andthe associated size and weight of the cutting chain itself.

Operation and functioning of the cradle 26 will now be described.Looking at FIGS. 3, 5, 14 and 16 to 18, it can be seen that a pluralityof hydraulic drive cylinders 82 are provided. The configuration of thehydraulic drive cylinders 82 can be seen clearly in FIG. 5 which showsthe hydraulic drive cylinders 82 having a pivoted connection 84 to arear wall 86 of the cradle 26. The cradle also has a central pivotedcoupling 88 to a fixed section of the machine 10. The cradle 26 isusually, during mixing/ground engagement, arranged with the hydraulicdrive cylinders 82 extended such that the back surface 86 is generallyvertical. This is a configuration shown in, say, FIG. 3.

To change the cutting chain on the ground engaging boom, the groundengaging boom is first lifted out of the ground and the hydraulic drivecylinders 82 are contracted. This causes the back surface 86 of thecradle to pivot about pivot point 88 such that the ground engaging boomwill then be rested within the chute 22, as described above. In thisconfiguration, the winch 80 can be activated as described with referenceto FIG. 19. The winch 80 is coupled to a longitudinal coupling membersuch as a rope or wire cable 90.

As can be seen in FIG. 19, the cable 90 extends back and forth around ashoulder 92 including a pulley wheel 94 around which the cable 90 isarranged to go. The cable 90 then extends backwards to the top of thecutting boom 36 and then forwards again to its end 96. The end 96 of therope or cable 90 may then be coupled to a replacement chain, the firstlink 98 of which is visible in FIG. 19. Replacing the cutting chain onthe boom is then simply achieved by activating the winch 80 to wind upthe rope 90 and thereby pull the chain 98 along the length of the groundengaging boom so as to entirely surround the both longitudinal sides ofthe boom and enable the chain to be fixed to it.

Once the link 98 reaches the position of the wheel 94 and shoulder 92,the rope 90 can be disconnected form the new chain 98 and the chainclosed in known ways. This for example could involve pulling round thethen distal (free) end of the chain that has not yet been pulled ontothe boom and connected to the end of the chain that has been pulled bythe rope or cable 90.

Looking still at FIG. 19, a tensioning mechanism is provided at the topend 36 of the boom 12. The tensioning mechanism 100 can be seen moreclearly in FIG. 20. The tensioning mechanism includes a pivot arm 102pivotally connected to the top end of the cutting boom via a pivot 104.A pinion 106 is provided for engagement with the chain 14. In use, thechain will pass between the pinion 106 and bracket 108 which acts as arestraining or containing mechanism for the chain on the tensioningsystem 100. The arm 102 is driven via a hydraulic drive system includingcylinders 110 which is pivotally mounted to a fixed pivot 112 on the topend of the boom and a fixed pivot 114 at the distal end of the arm 102of the tensioning mechanism 100. It will be appreciated that byextension of the hydraulic system 110, the arm 102 will be pivoted aboutpivot 104 relative to the boom, thereby tensioning the chain 14 aroundthe cutting boom 12.

The positioning of the chain adjustment mechanism on the ground engagingboom itself and importantly at the upper end of the boom, provides anumber of significant advantages. First, the tensioning mechanism isremote from the lower end of the ground engaging boom 12 which will beinteracting on a more regular basis with the earth formation beingtrenched. Secondly, this will ensure that the tensioning mechanism iskept away from the section of the boom that is likely to be most engagedwith the mixing agent, such as cement, when used as a mixing mechanism.It is known and conventional to provide such tensioning mechanisms atthe distal end of a ground engaging boom but it has been recognised thatby providing the tensioning mechanism at the top end of the cutting boomthe risk from the mixing agent being used setting and thereby possiblyrendering the tensioning mechanism ineffective, is significantlyreduced. The chain tensioning mechanism can be provided at the end orwithin 1-2 metres of the upper end of the boom. In some examples it ispositioned at a distance that is no more than 5% (or 10 or 15%) of theway along the length of the boom from the upper end thereof.

Finally, referring to the cradle 26, reference is made to FIG. 17. Thecradle 26 has a number of sections and the cradle can be opened orclosed to enable replacement and/or orientation of the ground engagingboom 12. The cradle in the example of FIG. 17 includes a pivoted doorsection 41 hingedly mounted via hinges 43 to a rear section 45. A pinion40 is provided which in use is arranged to mesh with rack 38 formed of aplurality of teeth on the ground engaging boom 12. The pinion 40 ispreferably driven by hydraulic power from main trencher body 34 that maybe derived from hydraulic power lines 15 (seen in FIG. 4, but not shownin FIG. 17). Thus by the interaction of the pinion 40 and rack 38 it canbe simply and reliably ensured that the direction of drive of the groundengaging boom is always aligned with the longitudinal axis of the groundengaging boom 12.

FIG. 18 shows the cradle 26 open and with the ground engaging boom 12removed. Thus the chute section 24 can be seen with flared ends 70 and71. The chute section is preferably provided as a fixed or integratedpart of the cradle and ensures that a continuous channel can be formedwith the chute 22 when the cradle is in a raised (folded), such as thatshown in FIG. 14.

The process of use of the machine described above will now be described.Initially, as shown in FIG. 6, the machine 10 may be provided on atrailer 120 for moving to an area where trenching is to be performed.The legs 20 are stowed so as not to generate unnecessary width of themachine during transport. Next, referring to FIG. 7, the legs 20 areextended and feet 48 arranged in position to receive and engage with thelegs. Any suitable form of fixing can be used to lock the feet 48temporarily to the legs 20. With the machine still on the trailer, thelegs 20 are jacked down such as to engage with the feet 48 as shown inFIG. 8. With the machine still on the trailer, tracks are coupled to themachine as shown in FIG. 9. With the legs and feet coupled as shown inFIG. 9A, the trailer can be removed leaving the machine 10 supported bythe legs and feet 48.

The machine is then lowered onto the ground as seen in FIG. 10 and thelegs 20 may be pulled back into the body of the machine as describedabove. FIG. 10 shows clearly the tracks now supporting the machine onthe ground with the feet 48 lifted such that they are no longer incontact with the ground.

Looking at FIG. 11, the hydraulic reels 30 are positioned on the machine10 and the cradle 26 is coupled to the rear of the machine. Next, asshown in FIG. 12, the chute 22 is fitted to the machine 10. The chutesection 24 is already fixed to the cradle 26.

Next, the mixing boom 12 is engaged with the cradle 26 as shown in FIG.13. A crane may be used to initially lift the ground engaging boom 12into position for engagement with the cradle 26. It is noted that thelegs 20 are extended at this stage, thereby providing stability to themachine during the assembly of the machine with the boom 12 and prior tothe boom actually engaging the ground and thereby providing stability ofits own.

The machine or rather the ground engaging boom is then lowered as shownin FIG. 14 by tilting back of the cradle 26. This is achieved asdescribed above by operation of the hydraulic controls via hydrauliccylinders 82 and the various pivot configurations provided on the backwall of the cradle. In this lowered position, connection of the chaindrive services, via tubes (hoses) from the hydraulic reels 30 ispossible.

As shown in FIG. 3, at this stage, the legs 20 are extended inpreparation for the fitting of the ground engaging boom 12, because thisis the point in the process at which the centre of gravity of themachine 10 is highest due to the vertical extent of the ground engagingboom 12 once there has been initial engagement in the cradle 26 (asshown in FIG. 13).

Once this process is achieved the ground engaging boom 12 is now readyfor folding down, (i.e. tilting backwards into the configuration shownin FIG. 14) for connection of the hydraulic supply lines 30. Thehydraulic supply lines 30 are coupled to the top of the boom for drivingthe cutting and mixing chain on the ground engaging boom. When the boomis then rotated back to the vertical configuration, as shown in FIG. 4,the ground engaging boom 12 is now ready for engagement with the ground.The legs 20 provide stability in this configuration.

As shown in FIG. 14A, the trenching operation has commenced with theboom driven down by use of the rack and pinion described above providedwithin the cradle 26 and on the boom itself. In the configuration ofFIG. 14A the ground engaging boom is partially submerged within theground. The boom is submerged to a desired depth which will produce adesired depth of trench. The legs 20 are raised and brought into thebody of the machine 10 as described above since they are not needed atthis stage for stability. With the chain operated by the chain driveservices the tracks of the machine can be controlled to control theformation of and the direction of the trench.

As shown in FIG. 15, the machine trenching is now at full depth with theboom deep underground and thereby providing an anchor and stability tothe machine 10 in operation.

Thus, the machine is able to operate with an extended boom whilst notrisking any lack of stability which could be catastrophic. This isparticularly the case in high-wind situations, which may be encounteredin some operating environments of trenching machines of this nature. Inparticular, when the machines are used in a river bank location, andwinds occur, which is likely, the risk of damage to the ground engagingboom and even the machine 10 itself is significant.

FIGS. 21 and 22 are, views of a machine 75 including an auxiliary powersupply 74. FIG. 21 is a simplified schematic view. In some situations,it is possible that the main hydraulic power supply provided as part ofthe machine 75 fails. This could occur for a number of reasons such as,for example, the supply runs out of fuel or one of the supply hosesbecomes damaged in use or breaks off from the machine. In thissituation, which may generally be thought of as failure of the mainhydraulic power supply, there is a risk to the machine and in particularthe ground engaging boom 12 which will typically be engaged with theground if the main hydraulic power supply is in operation providingpower to drive the pinion as described above. In such a situation, whenthe ground engaging boom is being used for, for example, mixing of amixing fluid with soil, the mixing fluid in the case of a mixing agentsuch as (but not limited to) cement could set thereby fixing the groundengaging boom in the trench that has been cut and filled with saidmixing agent/cement.

Typically, in the event of such a main power supply failure, it might beup to three days until a replacement can be obtained or indeed engineerscan be provided to fix the power failure on the machine 75. Inaccordance with one aspect of the present system, an auxiliary powersupply 74 is provided which can be used as a “hot stab” unit, i.e. whichis then able to immediately replace the main hydraulic power supply ofthe machine and provide the required power to remove the ground engagingboom 12 from its engaged position. The boom can then be extracted usingthe existing rack and pinion mechanism, described above, which ispowered by the auxiliary power unit 74.

By ensuring that the ground engaging boom 12 can be quickly and reliablyremoved from the ground in the event of main power supply failure, thisensures that the ground engaging boom will not become set in the grounddue to the delay that would otherwise be encountered.

The auxiliary power supply unit 74 may be referred to as a hot stab unitsince it will typically include a pair of hydraulic supply lines 76which are connected to hydraulic inputs in a power circuit of themachine to thereby drive the pinion and extract the ground engaging boomfrom its engaged position.

Looking at FIG. 21, which shows schematically, the arrangement of anauxiliary power supply unit, it can be seen that a lift motor 79arranged in normal use to receive power from supply lines 30 is providedwith sockets 81 to which the connectors 83 of the auxiliary supply unitcan be connected. Valves 85 on the supply lines 30 are closed and thelift motor 79 is instead powered by the hydraulic pump and supply unitvia inputs 81. The lift motor may be the motor that in use powers thepinion 40.

Looking at FIG. 22, the auxiliary power supply unit 74 is preferablyprovided as a separate unit. It may be provided entirely independently,but preferably is arranged coupled to the machine 75. The machine 75includes input sockets 81 arranged in normal use to be provided withpower from the existing hydraulic supply lines of the machine but, inthe event of main power supply failure, connectors 83 provided at thedistal ends of the supply line 76 maybe coupled to the inputs 81 topower the pinion and thereby, via interaction with the rack on theground engaging boom 12, cause the boom to be lifted out of the ground.

Embodiments of the present invention have been described with particularreference to the examples illustrated. However, it will be appreciatedthat variations and modifications may be made to the examples describedwithin the scope of the present invention.

1-44. (canceled)
 45. A trenching apparatus, comprising: a body moveableon the ground surface, a ground engagement boom associated with thebody, the boom being movable when engaged with the ground to form atrench; lifting means arranged to control and configure the groundengagement boom so as to enter the ground; in which the ground engagingboom is an endless chain ground-engaging boom, comprising a main bodyand a chain tensioner coupled to the main body at or close to the upperend thereof.
 46. Apparatus according to claim 45, in which the chaintensioner comprises an arm pivotally coupled to the main body of theground engagement boom.
 47. Apparatus according to claim 46, in whichthe arm is hydraulically controllable to move between a first closedposition in which its distal end is close to the main body and a seconddeployed position in which its distal end is moved away from the mainbody to tension a chain arranged on the ground engagement boom. 48.Apparatus according to any of claim 47, comprising an endless chainmounted on the main body, in which the chain is a cutting or mixingchain.
 49. (canceled)
 50. Apparatus according to claim 45, in which theground engagement boom weighs between 10 and 20 tonnes.
 51. Apparatusaccording to claim 46, in which the arm comprises a pinion at its distalend to gearingly engage with the chain as it is driven around the groundengagement boom.
 52. Apparatus according to claim 46, in which the armis between 1 and 3 metres long.
 53. Apparatus according to claim 47, inwhich the arm has a plurality of hydraulic drive cylinders provided tohydraulically control the position of the arm with respect to the body.54. Apparatus according to claim 45, in which the chain tensioner ispositioned with respect to the main body such that when the groundengaging boom is fully engaged with the ground the chain tensioner isabove ground surface.
 55. A ground engaging boom for use with atrenching apparatus, wherein the ground engaging boom is an endlesschain ground engaging boom, in which the ground engaging, comprises amain body and a chain tensioner coupled to the main body at or close tothe upper end thereof.
 56. A ground engaging boom according to claim 55,in which the chain tensioner comprises an arm pivotally coupled to themain body of the ground engagement boom.
 57. A ground engaging boomaccording to claim 56, in which the arm is hydraulically controllable tomove between a first closed position in which its distal end is close tothe main body and a second deployed position in which its distal end ismoved away from the main body to tension a chain arranged on the groundengagement boom
 58. A ground engaging boom according to claim 57,comprising an endless chain mounted on the main body.
 59. A groundengaging boom according to claim 58, in which the chain is a cutting ormixing chain.
 60. A ground engaging boom according to claim 55, in whichthe ground engagement boom weighs between 10 and 20 tonnes.
 61. A groundengaging boom according to claim 56, in which the arm comprises a pinionat its distal end to gearingly engage with the chain as it is drivenaround the ground engagement boom.
 62. A ground engaging boom accordingto claim 56 11, in which the arm is between 1 and 3 metres long.
 63. Aground engaging boom according to claim 57, in which the arm has aplurality of hydraulic drive cylinders provided to hydraulically controlthe position of the arm with respect to the body.
 64. A ground engagingboom according to claim 55, in which the chain tensioner is positionedwith respect to the main body such that when the ground engaging boom isfully engaged with the ground the chain tensioner is above groundsurface.
 65. A method of varying tension in the chain of aground-engaging boom of trenching apparatus, in which the trenchingapparatus comprises a body moveable on the ground surface and a groundengagement boom associated with the body, the boom being movable whenengaged with the ground to form a trench, the method comprising:controlling the tension of the chain using a chain tensioner coupled tothe main body of the ground engaging boom at or close to the upper endthereof. 66-83. (canceled)